There has been known a wiring board including a plurality of wiring layers, a plurality of insulating layers, and an electrode member made of a conductive material. The electrode member is embedded in the wiring board while having an exposed portion on a side surface intersecting the plurality of wiring layers and the plurality of insulating layers.
There has been known an electronic component-built in board including a multilayered board in which an insulating layer and an internal circuit layer are laminated, a via formed in the insulating layer to electrically connect internal circuit layers to each other, a cavity formed in one surface of the multilayered board, a first electronic component, and a bump pad. The first electronic component is inserted into the cavity. The bump pad is formed on the surface of the cavity facing the first electronic component while the insulating layer and the via are formed to be exposed on a side wall of the cavity.
However, since a light emitting element and an optical waveguide are separate parts, it is difficult to accurately provide the light emitting element in the optical waveguide.
The followings are reference documents.    [Document 1] Japanese Laid-Open Patent Publication No. 2012-186301 and    [Document 2] Japanese Laid-Open Patent Publication No. 2016-136615.